Turbine engines are used as the primary power source for various kinds of aircraft. Turbine engines may also serve as auxiliary power sources that drive air compressors, hydraulic pumps, and industrial electrical power generators. Most turbine engines generally follow the same basic power generation procedure. Specifically, compressed air is mixed with fuel and burned, and the expanding hot combustion gases are directed against stationary turbine vanes in the engine. The stationary turbine vanes turn the high velocity gas flow partially sideways to impinge onto turbine blades mounted on a rotatable turbine disk. The force of the impinging gas causes the turbine disk to spin at a high speed. Some turbine engines, such as jet propulsion engines, use the power created by the rotating turbine disk to draw more air into the engine, and the high velocity combustion gas is passed out of the turbine engine to create a forward thrust. Other engines use this power to turn one or more propellers, electrical generators, or other devices.
Because fuel efficiency improves as engine operating temperatures increase, turbine components such as engine blades and vanes are typically exposed to increasingly hotter gas temperatures. However, the ability to operate at these extreme temperatures is limited by the mechanical strength of the materials from which the turbine components are manufactured, as they may undesirably oxidize and/or corrode when exposed to the combustion gases.
To improve oxidation and/or corrosion resistance and decrease surface temperature of the turbine components, a protective thermal barrier coating (TBC) may be applied on the component. For example, ceramic thermal barrier coatings (TBCs) are used on turbine components to increase temperature capability and efficiency of gas turbines. One ceramic TBC consists of a layer of 7-8 weight percent yttria-stabilized zirconia (7YSZ) deposited by an electron beam physical vapor deposition (EB-PVD) process or by plasma spray onto a metallic bond coat formed over the turbine component. Although 7YSZ is suitable for use as a TBC for certain engine operating temperature ranges, it may not be suitable for use in higher temperature ranges. In such case, other more advanced ceramic TBCs, such as those that consist of lanthanide-base oxides with the general formula A2B2O7, including but not limited to gadolinium zirconate, Gd2Zr2O7 or neodymium zirconate, Nd2Zr2O7, may be employed. Another example is fully-stabilized cubic zirconia, such as 20 weight percent yttria-stabilized zirconia (20YSZ). These more advanced ceramic TBCs have lower thermal conductivity and, therefore, may provide better thermal insulation as compared to 7YSZ. However, these oxides have significantly lower fracture toughness than 7YSZ, which limits TBC cyclic life and erosion resistance.
Accordingly, there is a need for an improved TBC that has both high fracture toughness and a reduced thermal conductivity, as compared to the aforementioned conventional TBCs. Additionally, it is desirable for the improved TBC to also be capable of exhibiting corrosion resistance, sintering resistance, and/or high temperature stability when subjected to the combustion gases of the turbine component. Furthermore, other desirable features and characteristics of the inventive subject matter will become apparent from the subsequent detailed description of the inventive subject matter and the appended claims, taken in conjunction with the accompanying drawings and this background of the inventive subject matter.